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United States Patent |
6,172,490
|
Antoszkiewicz
|
January 9, 2001
|
Precise rail tracking method for powering dual voltage integrated circuits
Abstract
A rail tracking system and method for providing precise tracking of voltage
levels to a dual supply voltage Integrated Circuit. A switch mode DC--DC
voltage regulator is used to derive the lower of the two voltage levels
from the higher level. The switch mode regulator employs a pulse width
modulator (PWM) to derive the lower voltage level. A separate supply
source is utilized to power the PWM and the timing of the supply voltage
is such that the PWM has reached steady state before the higher voltage
level is provided to the regulator.
Inventors:
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Antoszkiewicz; Wojciech (Kanata, CA)
|
Assignee:
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Alcatel Networks Corporation (Kanata, CA)
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Appl. No.:
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456392 |
Filed:
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December 8, 1999 |
Current U.S. Class: |
323/267; 323/269; 323/274 |
Intern'l Class: |
G05F 001/577; G05F 001/40; G05F 001/44 |
Field of Search: |
323/267,269,273,274
|
References Cited
U.S. Patent Documents
4087759 | May., 1978 | Iwamatsu | 330/262.
|
4472687 | Sep., 1984 | Kashiwagi et al. | 330/297.
|
5200711 | Apr., 1993 | Anderson et al. | 330/267.
|
5543753 | Aug., 1996 | Williamson | 330/297.
|
5606289 | Feb., 1997 | Williamson | 330/297.
|
5898340 | Apr., 1999 | Chatterjee et al. | 330/351.
|
6011382 | Jan., 2000 | Littlefield et al. | 323/222.
|
Other References
Power Trends, Inc. application note entitled: "Integrated Switching
Regulators, DC to DC Converters".
|
Primary Examiner: Wong; Peter S.
Assistant Examiner: Vu; Bao Q.
Attorney, Agent or Firm: Marks & Clerk
Claims
What is claimed is:
1. A rail tracking method for providing dual voltage levels to first and
second voltage rails on an integrated circuit (IC) comprising:
providing a first voltage to said first voltage rail;
providing said first voltage to a voltage regulator having conversion means
to derive a second voltage for said second voltage rail; and
providing a supply voltage to said conversion means whereby said supply
voltage is provided before said first voltage is provided to said voltage
regulator.
2. The method according to claim 1 wherein said conversion means uses a
pulse width modulator (PWM) to derive said second voltage from said first
voltage.
3. A system for providing rail tracking of dual voltage levels to first and
second voltage rails on an integrated circuit (IC) comprising:
first voltage means to supply a first voltage level to said first voltage
rail;
a voltage regulator having means to receive said first voltage level;
conversion means in said voltage regulator to derive a second voltage
level for said second voltage rail from said first voltage level; and
a supply voltage means to supply a supply voltage to said conversion means
wherein said supply voltage is supplied to said conversion means before
said first voltage is supplied to said voltage regulator.
4. A system as defined in claim 3 wherein said conversion means includes a
pulse width modulator (PWM).
5. A system as defined in claim 4 further including a backward tracking
diode between said second voltage rail and said first voltage rail.
6. A system as defined in claim 5 wherein said first voltage level supplies
input/output functions on said IC and said second voltage level powers a
core processor on said IC.
7. A system as defined in claim 6 wherein said supply voltage is supplied
by a DC--DC switch-mode power supply.
8. A system for providing rail tracking to an Integrated Circuit (IC)
wherein said IC performs multiple functions requiring dual operating
voltage levels; said system comprising:
a first DC--DC power supply to supply a first voltage level to said IC;
a voltage regulator circuit employing a switch mode converter to receive
said first voltage level and to derive therefrom a second voltage level
for said IC; and
a second DC--DC power supply to supply operating voltage to said switch
mode converter;
whereby said second DC--DC power supply supplies said operating voltage to
said switch mode converter such that said converter is operational before
said first voltage level to derive said second voltage level is supplied
to voltage regulator circuit.
9. A system as defined in claim 8 wherein said switch mode converter
employs a pulse width modulator to derive said second voltage level.
10. A system as defined in claim 8 wherein said voltage regulator circuit
has a separate connection for receiving said supply voltage.
Description
FIELD OF THE INVENTION
This invention relates to integrated circuits having dual supply voltage
requirements and, more particularly, to a system and method for accurately
controlling the dual supply voltage levels.
BACKGROUND OF THE INVENTION
Many large scale integrated circuits contain multiple components providing
different functionality and require two different supply voltage levels to
operate. One such integrated circuit would include, for example, a core
processor and input/output functions on the same silicon substrate, but
operating from two different voltage levels. During startup, steady state,
shut down and under fault conditions, the interaction between these
voltages must meet strict requirements to ensure proper operation and to
prevent damage to the integrated circuit. The techniques used to ensure
proper interaction of these voltage levels all fall under the class of
methods known as "Rail Tracking".
In a dual supply voltage mode scenario, typically, the larger of the two
voltage rails will supply the input/output function, and the smaller of
the two is used to power the core processor. The larger of the two voltage
levels is supplied to the input/output functionality of the integrated
circuit, and to a voltage regulator which derives the second or lower
voltage level for use in powering the core processor.
The task of the voltage regulator consists of keeping the voltage on the
output constant in a defined output range. One form of voltage regulator
comprises a switch mode power supply. A switch mode power supply usually
comprises a pulse width modulator (PWM), a power switch, a rectifier and
an output filter. The pulse width modulator controls the power switch
which converts an input voltage into pulsed DC voltage with variable duty
cycle which in effect maintains constant voltage on the output of the
filter circuit. In conventional voltage regulator voltage to power the PWM
circuit is derived from the regulator's input voltage.
Because the PWM circuit requires a finite period to achieve steady state
conditions there is an initial period between the time that the voltage is
supplied to the regulator input and the time in which the output is fixed
at the second voltage level. During this time the voltage difference
between the input/output voltage and output core voltage may exceed
maximum allowable limits causing damage to the integrated circuit.
A prior art method dealing with this problem is disclosed in Power Trends
application note PT5000/6000 SIP Series (Integrated Switching Regulators
DC--DC Converters). In this prior art solution, the voltage regulator is
bypassed by a number of series connected diodes and a small resistor which
are connected between the input/output voltage level and the core
processor voltage. The series-connected diodes limit the difference
between the two voltage levels as will be discussed in greater detail
hereinafter.
There are shortcomings to this prior art method which render it
unacceptable in certain circumstances. For example, as the steady state
difference between the input/output voltage and the core processor voltage
approaches the maximum allowable voltage difference, the tolerance on the
diode voltage drop becomes critical. This tolerance is difficult to
control inasmuch as the voltage drop across the diode junction is highly
current and temperature dependent. Additionally, the tracking voltage
difference can be set only with the resolution of each single junction
voltage drop which typically equals approximately 0.6 volts or 0.3 volts
for Schottky technology. Additionally, the series-connected diodes
bypassing the voltage regulator negate any overcurrent protection provided
by the voltage regulator. In addition, the diodes themselves can be easily
damaged if the regulator fails as all of the current associated with the
second voltage level will now flow through the diodes.
SUMMARY OF THE INVENTION
Accordingly, there is a requirement for an improved rail tracking system
and method for powering a dual voltage integrated circuit.
Therefore, in accordance with a first aspect of the present invention there
is provided a rail tracking method for providing dual voltages levels to
first and second voltage rails on an integrated circuit (IC) comprising:
providing a first voltage to the first voltage rail; providing the first
voltage to a voltage regulator having conversion means to derive a second
voltage for the second voltage rail; and providing a supply voltage to the
conversion means whereby the supply voltage is provided before the first
voltage is provided to the voltage regulator.
In accordance with a second aspect of the present invention there is
provided a system for providing rail tracking of dual voltage levels to
first and second voltage rails on an integrated circuit comprising: first
voltage means to supply a first voltage level to the first voltage rail; a
voltage regulator having means to receive the first voltage level;
conversion means in the voltage regulator to derive a second voltage level
for the second voltage rail from the first voltage level; and a supply
voltage means to supply a supply voltage to the conversion means wherein
the supply voltage is supplied to the conversion means before the first
voltage is supplied to the voltage regulator.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in greater detail with reference to the
attached drawings wherein:
FIG. 1 is a typical power circuit for dual voltage integrated circuits;
FIG. 2 is a diode rail tracking circuit according to the prior art;
FIG. 3 is a linear series pass regulator rail tracking circuit;
FIG. 4 is a circuit diagram of a precise rail tracking methodology
according to the present invention; and
FIG. 5 is an example of a block diagram of a practical implementation of
the tracking method according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates a typical power circuit for a dual voltage integrated
circuit. Integrated circuit 12, which according to the present invention
has a requirement for dual supply voltage levels, namely, a first voltage
level for the input/output voltage (Vi/o) and a second voltage level for
the core processor (Vcore). As discussed previously Vi/o is at a higher
voltage level than Vcore. An input voltage (Vin) is provided by a power
supply (not shown) to Vi/o and to the input of a voltage regulator 14.
Voltage regulator 14 derives the Vcore voltage level from Vin. Typically,
voltage regulator 14 employs switch mode topology to achieve the voltage
conversion. The key element of the switch mode topology is a pulse width
modulator as discussed previously. The key aspect, however, is that the
voltage regulator output voltage reaches its steady state value, i.e.
Vcore, only after initial stabilizing period has passed. As noted
previously, during this stabilizing period, the voltage difference between
the input/output voltage and the output core voltage may exceed maximum
allowable limits causing damage to the integrated circuit.
The prior art solution to this problem is illustrated in FIG. 2 wherein
voltage regulator 14 is bypassed by series-connected diodes 16, 18 and 20,
and resistor 22. Typically, fuse 24, will protect the voltage regulator
and downstream components.
According to the prior art method, the series-connected diodes are selected
to provide a voltage drop across the voltage regulator such that the
voltage difference between the input and at the core cannot exceed the
maximum specified value. In FIG. 2, diodes 16, 18 and 20, limit the
difference between Vi/o and Vcore. As discussed previously, there are
shortcomings to the method illustrated in FIG. 2 which limits practical
implementations of the concept.
A rail tracking method developed by Newbridge Networks Corporation uses a
linear series pass regulator connected between the input Vi/o and the
output Vcore of the regulator. This method has proven to be effective when
high precision tracking (1.6V maximum difference between Vi/o and Vcore,
while the normal operation difference is only 1.3V) is required with high
currents (6 to 20A). A circuit illustrating this rail tracking method is
shown in FIG. 3. Operational amplifier 30 controls power transistor 38
which, in turn, provides Vcore during the time it takes regulator 14 to
startup. During the initial period, operational amplifier 30 is controlled
by V reference 32 until the output across voltage divider 34/36 reaches
the steady state value. Resistor 40 reduces power dissipation in
transistor 38, and diode 42 provides backward tracking during turnoff. An
additional voltage monitoring network, (not shown) is required to protect
resistor 40 and transistor 38 in the case of a failure of the regulator
14.
Although the rail tracking method shown in FIG. 3 is effective, multiple,
real estate consuming, power components are required in addition to the
standard regulator.
Regulator 14 in the prior art and in the embodiment of FIG. 3 typically
employs a switch mode topology to achieve voltage conversion. The key
element of this topology is the pulse width modulator (PWM) as previously
discussed. The regulator will only produce the required output voltage
after the PWM is operational. As discussed previously, the supply voltage
for the PWM is derived from the regulator input voltage. Accordingly,
there is an inherent delay between the voltage being applied to the
regulator input and the PWM being operational. This accounts for the delay
between Vi/o and Vcore.
The preferred embodiment of the present invention is illustrated in the
circuit diagram of FIG. 4. The basis of this invention relies on the PWM
power supply being connected prior to the regulator input voltage being
applied. As a result, the regulator output voltage will track, with no
delay, the regulator input voltage. This ensures true tracking between
regulator input and output voltages which correspond to the true tracking
between Vi/o and Vcore.
As shown in FIG. 4, voltage regulator 14 includes pulse width modulator 50,
which is supplied by supply voltage through input 52. In accordance with
the basic concept of the invention, supply voltage is provided through
input 52 prior to Vi/o being supplied to the regulator. In this way, the
pulse width modulator has reached steady state condition before Vi/o is
supplied and hence, the regulator output voltage (Vcore) will precisely
track the regulator input voltage. As shown in FIG. 4, the PWM supply
voltage is an external voltage not necessarily related to the regulator
input voltage.
The Schottky diode 54 provides backward tracking during turnoff. An
additional voltage monitoring network (not shown) may be used to protect
the integrated circuit in case of failure of the regulator.
The tracking method provided by the embodiment of FIG. 4 offers the
following benefits over those previously described. First, this method
provides precise rail tracking inasmuch as the pulse width modulator is
fully operational before the regulator input voltage is supplied.
Secondly, no additional power components are required which results in
lower board space, lower cost of the design, and increased reliability.
Further, the regulator current limit is not bypassed as was the case in
the prior art method.
The block diagram of FIG. 5 shows an example of a practical application of
the tracking method of the present invention as implemented in a practical
design.
Four isolated DC--DC converters are used to provide power to the system.
Three of these converters (3.3V and 2.times.2.5V outputs) are standard
modules which operate in the input voltage range 36 to 75V. The fourth
one, the 5V output, operates over a wide input range 18 to 75V, and is
designed to start faster than the remaining three major converters.
The main function of the +5V converter is to provide early supply voltage
for the monitoring circuit 60 which, via On/Off pins controls the major
converters. As shown, the early 5V converter is not part of the On/Off
loop. The rail tracking in the system is required between the 3.3V and
2.5V rails and between the 3.3V Vi/o and 2.0V Vcore for the dual power IC.
Tracking between high current rails (3.3V/60A and 2.5V/20A) has been
provided using the linear series pass regulator circuit as illustrated in
FIG. 3. The tracking method according to the preferred embodiment of FIG.
4 is used for providing tracking between the 3.3V and 2.0V rail for the
dual power IC. The 3.3V to 2.0V module is a non-isolated, DC--DC switch
mode power supply. According to the preferred embodiment of the invention,
the pin to supply the supply voltage to the pulse width modulator is
isolated in order that voltage from the early 5V supply can be connected
directly to the pulse width modulator.
Although example embodiments of the invention have been disclosed and
illustrated, it will be apparent to one skilled in the art that variation
to the basic concept can be implemented. Particularly the input/output and
core voltage levels and the DC--DC module type may be different. It is to
be understood, however, that such variations will fall within the true
scope of the invention as defined by the appended claims.
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